Brain Changes Associated with Casual Marijuana Use

Posted on April 21, 2014 at 4:37 pm

According to a recent study, the size and shape of two brain regions involved in emotion and motivation may differ in young adults who smoke marijuana at least once a week.[1] Recreational marijuana use may lead to these changes; therefore, understanding the long-term effects of low to moderate marijuana use is critical.1

The most commonly used illicit substance in the United States, and estimated 18.9 people currently use marijuana, according to the most current analysis of the National Survey on Drug Use and Mental Health.1 Marijuana use is associated with motivation, attention, learning, and memory impairments, and previous studies found that repeated exposure can cause structural changes in brain regions involved with these functions.1 However, less is known about low to moderate marijuana use and how it affects brain structure.1

Jodi Gilman, PhD, Anne Blood, PhD, and Hans Breiter, MD, of Northwestern University and Massachusetts General Hospital/Harvard Medical School used MRIs to compare the brains of 18- to 25-year-old participants who reported smoking marijuana at least once per week and those with no history of marijuana use.1 Although, psychiatric evaluations found that users were not dependent on the drug, imaging data revealed that they had significant brain differences.1 The nucleus accumbens, the region known to be involved in reward processing, was larger and altered in shape and structure in those who used marijuana casually.1

“This study suggests that even light to moderate recreational marijuana use can cause changes in brain anatomy,” said Carl Lupica, PhD, who studies drug addiction at the National Institute on Drug Abuse. “These observations are particularly interesting because previous studies have focused primarily on the brains of heavy marijuana smokers, and have largely ignored the brains of casual users.”1

Researchers also compared the size, shape, and density of the nucleus accumbens and the amygdala, the region that plays a role in emotion, in 20 marijuana users and 20 non-users.1 It was found that the more marijuana users reported using, the greater the abnormalities in the two brain regions.1

“This study raises a strong challenge to the idea that casual marijuana use isn’t associated with bad consequences,” said Breiter.1

[1] Society for Neuroscience (SfN). (2014, April 15). Brain changes associated with casual marijuana use in young adults: More ‘joints’ equal more damage. ScienceDaily. Retrieved April 18, 2014 from www.sciencedaily.com/releases/2014/04/140415181156.htm